The present disclosure generally relates to treatment fluids containing a perfluorinated carboxylic acid for use in subterranean formation operations, and, more specifically, to perfluorinated carboxylic acids capable of, among other things, generating hydrofluoric acid in downhole environments.
Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations may include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof, refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof, unless otherwise specified herein. More specific examples of illustrative treatment operations can include fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, consolidation operations, and the like.
Downhole acidizing operations and other dissolution operations may be used to stimulate a subterranean formation to increase production of a hydrocarbon resource therefrom. During an acidizing operation or a like dissolution operation, an acid-soluble material in the subterranean formation may be dissolved by one or more acids to expand existing flow pathways in the subterranean formation, to create new flow pathways in the subterranean formation, and/or to remove acid-soluble precipitation damage in the subterranean formation, thereby stimulating the formation's production capabilities. Introduction of an acidizing fluid to a subterranean formation may take place at matrix flow rates without fracturing of the formation matrix or at higher injection rates and pressures to fracture the formation. The acid-soluble material being dissolved by the acid(s) may be part of or formed from the native formation matrix or have been deliberately introduced into the subterranean formation in conjunction with a stimulation or like treatment operation (e.g., bridging agents, proppants, or gravel particulates). Illustrative substances within the native formation matrix that may be dissolved by an acid may include, but are not limited to, silicates and aluminosilicates, and carbonates which may be present alone or in combination with one another in formations of mixed mineralogy. Other substances may also be dissolved during the course of performing an acidizing operation, and the foregoing substances should not be considered to limit the scope of substances that may undergo acidization.
Siliceous formations may include minerals such as, for example, zeolites, clays, feldspars, and combinations thereof. As used herein, the term “siliceous” refers to a substance having the characteristics of silica, including silicates and/or aluminosilicates. Among other acids, hydrofluoric acid, a mineral acid, may react very readily with siliceous materials to promote their dissolution. Often, another mineral acid or an organic acid may be used in conjunction with hydrofluoric acid to maintain a low pH state as the hydrofluoric acid becomes spent during dissolution of a siliceous material, where the low pH state helps promote continued solubilization of the siliceous material. Additionally, a chelating agent may often be included with the acid to effectively dissolve the siliceous material, the chelating agent capable of complexing siliceous material for the acid to act upon. Many types of siliceous formations can also contain varying amounts of carbonate materials. Most sandstone formations, for example, contain about 40% to about 98% sand quartz particles (i.e., silica), bonded together by various amounts of cementing materials, which may be siliceous in nature (e.g., aluminosilicates or other silicates) or non-siliceous in nature (e.g., carbonates, such as calcite). When siliceous materials are co-present with carbonate materials, significant precipitation issues can sometimes be encountered, as discussed below.
Carbonate formations may contain minerals that comprise a carbonate anion (e.g., calcite (calcium carbonate), dolomite (calcium magnesium carbonate), siderite (iron carbonate), and the like, and combinations thereof). When acidizing a carbonate formation, the acidity of the treatment fluid alone may often be sufficient to solubilize the carbonate material by decomposing the carbonate anion to carbon dioxide and leeching a metal ion into the treatment fluid. Both mineral acids (e.g., hydrochloric acid) and organic acids (e.g., acetic and formic acids) may be used to treat a carbonate formation, often with similar degrees of success. Since it is relatively inexpensive, hydrochloric acid is very commonly used, typically in concentrations up to about 28% by volume. Like acid dissolution operations in siliceous formations, a chelating agent may often be included with the acid to effectively dissolve carbonate materials in carbonate formations, the chelating agent capable of complexing the carbonate material for the acid to act upon.
In some instances, it can be desirable to remove a carbonate material from a siliceous formation prior to acidizing the siliceous material therein to decrease the occurrence of precipitation in the subterranean formation. For example, calcium ions liberated from the carbonate material can react readily with fluoride ions from hydrofluoric acid to form highly insoluble calcium fluoride, which can often be more damaging to the subterranean formation than if the acidizing operation had not been performed in the first place. Different metal ions liberated from other carbonate materials can also be problematic in this regard. Metal ions liberated from aluminosilicates and other metal-containing siliceous materials may also be problematic in this regard.
Acids are typically included in treatment fluids to perform acidizing operations to dissolve and remove siliceous or carbonate material. The acid may be included prior to introducing the treatment fluid into the formation or on-the-fly during a treatment operation. As used herein, the term “on-the-fly” refers to performing an operation during a subterranean treatment that does not require stopping normal operations. In both instances, the acid must be handled either alone or as part of the treatment fluid. Additionally, in typical acidizing or dissolution treatment operations, the acid functions effectively only at particularly low pH ranges, such as those below about 4, or about 3.5. Often, treatment fluids alone or after being subjected to downhole conditions become more basic in pH. As mentioned earlier, additional acidic fluids may be included to ensure that low pH ranges are achieved. However, such additional acids may increase any operational hazards associated with handling the treatment fluid and acidic components.